Escapement devices, or sequencers as they may be termed, are used with conveyor systems to control the travel of articles along the conveyor. Many times, the escapement device is employed to permit the passage of an article along the conveyor when a downstream station is prepared to receive the article. Escapement devices also are employed to control the spacing between successive articles along the conveyor. Such spacing may be required to accommodate subsequent processing steps downstream on the conveyor; or to otherwise regulate the timing sequence of the articles, as when meshing with other conveyor flows.
Escapement devices known in the art have significant limitations. Many are specifically manufactured to handle articles of one size, or with very little size variation. Generally, these types of escapement devices employ star wheels or turnstiles to positively engage the articles and discharge them downstream on the conveyor.
Other escapement devices employ one or more movable barriers or gates which selectively are positioned within the path of the articles on the conveyor. Such gates may be interposed from above, below or at the side of the conveyor. These gates generally are suitable to block articles of various sizes on the conveyor. However, they do not serve forcefully to eject an article downstream. Rather, the movement of the conveyor belt, or the force of gravity on inclined roller conveyors, must be relied upon to move the article.
Due to slippage between the article and the conveyor belt, or the effect of friction in the conveyor rollers, the acceleration of the article from its stopped position upstream of the gate may vary significantly from article to article. As a result, it is quite difficult to obtain uniform spacing of articles along the conveyor, which may then jeopardize downstream operations. Furthermore, the articles may become stuck in the path of the gate, causing a restriction which ultimately may lead to a shutdown of the conveyor line.
Despite the various escapement devices known in the art, none is available which is capable of handling articles of varying sizes at the same time, for example, handling a plurality of articles where some might be up to twice the size of others, while at the same time providing forced discharge of the articles from the escapement device to ensure appropriate spacing of the articles. Moreover, no device is available which is capable of handling tires ranging in size from approximately 22 inches (55.9 cm) to approximately 36 inches (91.4 cm) at the same time.